In the recovery of oil from oil-containing formations, it is usually possible to recover only minor portions of the original oil-in-place by so-called primary recovery methods which utilize only natural forces. To increase the recovery of oil a variety of supplementry recovery techniques are employed. These techniques include waterflooding, miscible flooding, thermal recovery, and steam stimulation.
One of the problems encountered in producing wells in heavy oil reservoirs, with or without steam stimulation, is that early in the production phase, it is desirable, and often necessary, to complete and produce the well from near the top of the producing interval. This is desirable or necessary because the steam rises to the top of the producing zone due to gravity override, providing stimulation for oil production. If the well is not completed at the top, it may not respond soon enough to provide an economically feasible operation. Later on, as some of the oil is produced, the steam will simply breakthrough into the wellbore, moving only a minimal amount of oil with it, and making the overall recovery process very inefficient. It then becomes necessary to recomplete the well one or more times lower in the producing section. Recompletion is an expensive operation, and the economics of steam aided production is adversely affected by the need for recompletions. For this reason, methods have been disclosed for selectively plugging high permeability streaks and channels in reservoirs.
U.S. Pat. No. 4,074,757 to Felber et al. discloses a method for the selective plugging of undesirable high permeability streaks and channels in oil bearing reservoirs during temperature (250.degree. F. or higher) injection recovery processes such as steam flooding, underground combustion flooding or a naturally occurring high temperature reservoir, or the like. Improved sweep efficiency is obtained by injecting a gel-forming solution consisting essentially of sodium or ammonium lignosulfonate and water or brine in the absence of other gelation promoters and then allowing the high temperatures of the underground formation to promote gelation. To ensure that the injected gel-forming solution is confined largely to the high permeability zone of the formation, it is necessary to isolate the offending, high-permeability zone by one or more packers or plug back procedures. However, this method does not ensure that there is no tendency for the gel-forming solution to flow into the low permeability zones of the formation.
Other U.S. patents teaching the use of polymers that are injected as monomer solutions and polymerize in-situ to effect plugging of highly permeable zones include U.S. Pat. No. 4,637,467 to Shaw et al. and U.S. Pat. No. 4,461,351 to Falk. These processes are not selective because the monomers before they polymerize can penetrate into high as well as the low permeability zones of the formation and packers are required to inject the monomer into selected portions of the formation.
Therefore, what is needed is a method of forming a solid gel in areas of a formation which have been heated to a temperature above 300.degree. F. so as to minimize well recompletions.